SLOW-MOLECULE DETECTION IN DOPPLER-FREE 2-PHOTON SPECTROSCOPY

We present the first observation of optical detection of slow molecule s by using Doppler-free two-photon spectroscopy (DFTPS). We obtained a linewidth of 280 Hz (HWHM) which is 23 times narrower than the transi t broadening for the most probable velocity class. Slow-molecule two-p hoton resonances are, thus, very promising candidates for frequency st andards in the infrared. This experiment was performed in the 2 nu(3) band of SF6 in the 10 mu m spectral region. It reveals also for the fi rst time a magnetic hyperfine structure in molecular DFTPS.